CN116027403A - Imaging method and device based on wave field decomposition - Google Patents
Imaging method and device based on wave field decomposition Download PDFInfo
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Abstract
The embodiment of the specification discloses an imaging method and device based on wave field decomposition. Generating a source end wave field by forward continuation according to forward numerical simulation, and generating a wave field of a wave point end by backward continuation of the seismic record; decomposing the wave field of the seismic source end to obtain a left lower wave field, a right lower wave field, a left upper wave field and a right upper wave field of the seismic source end, and decomposing the wave field of the wave point end to obtain a left lower wave field, a right lower wave field, a left upper wave field and a right upper wave field of the wave point end; obtaining a positive dip angle reflecting layer according to the left lower wave field of the seismic source end, the right upper wave field of the wave detection point end, the right lower wave field of the seismic source end and the left upper wave field of the wave detection point end, and obtaining a negative dip angle reflecting layer according to the left upper wave field of the seismic source end, the right lower wave field of the wave detection point end, the right upper wave field of the seismic source end and the left lower wave field of the wave detection point end; and correlating the positive inclination angle reflecting layer and the negative inclination angle reflecting layer to obtain a final diffracted wave imaging result.
Description
Technical Field
The present description relates to the field of exploration geophysics, and in particular to an imaging method and apparatus based on wavefield decomposition.
Background
Along with the continuous deep development of oil and gas field exploration at home and abroad, the focus of oil and gas exploration is oriented to the field of unconventional resources with complex structure, small scale and deep burial depth, such as deep land, deep sea and the like. Typical reservoirs of unconventional oil and gas are mainly: carbonate rock, river sand, high and steep structure, compact sandstone and the like, most of the reservoirs are characterized by pores, holes, cracks and combinations thereof, and the reservoirs are rich in diffraction wave information in the seismic exploration process.
Conventional seismic data processing typically estimates the velocity of the medium from primary reflected wave information, images subsurface continuous reflection layers and geologic formations, but the seismic response of subsurface small scale heterogeneous formations is typically represented by diffracted wave information, which cannot be effectively utilized with the precise information carried by the diffracted waves.
Based on this, a solution is needed that can accurately image the diffractor.
Disclosure of Invention
The present invention aims to provide a solution that can accurately image a diffractor.
In order to solve the technical problems, the invention adopts the following technical scheme:
in a first aspect, there is provided an imaging method based on wavefield decomposition, comprising: forward continuation is carried out according to forward modeling to generate a source end wave field, and backward continuation is carried out on the seismic record to generate a wave field of a wave point end; decomposing the wave field of the seismic source end to obtain a left down wave field of the seismic source end
Right lower wave field->
Left upper wave field->
And top right wavefield->
And decomposing the wave field at the wave point end to obtain a left lower wave field of the wave field at the wave point end +.>
Right lower wave field->
Left upper wave field->
And top right wavefield->
Obtaining a positive dip angle reflecting layer according to the left lower wave field of the seismic source end, the right upper wave field of the wave detection point end, the right lower wave field of the seismic source end and the left upper wave field of the wave detection point end, and obtaining a negative dip angle reflecting layer according to the left upper wave field of the seismic source end, the right lower wave field of the wave detection point end, the right upper wave field of the seismic source end and the left lower wave field of the wave detection point end; and correlating the positive inclination angle reflecting layer and the negative inclination angle reflecting layer to obtain a final diffracted wave imaging result.
In a second aspect, there is provided a computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements the method according to the first aspect when executing the program.
The above-mentioned at least one technical scheme that this description embodiment adopted can reach following beneficial effect: generating a source end wave field by forward continuation according to forward numerical simulation, and generating a wave field of a wave point end by backward continuation of the seismic record; decomposing the wave field of the seismic source end to obtain a left down wave field of the seismic source end
Right lower wave field->
Left upper wave field->
And top right wavefield->
And decomposing the wave field at the wave point end to obtain a left lower wave field of the wave field at the wave point end
Right lower wave field->
Left upper wave field->
And top right wavefield->
Obtaining a positive dip angle reflecting layer according to the left lower wave field of the seismic source end, the right upper wave field of the wave detection point end, the right lower wave field of the seismic source end and the left upper wave field of the wave detection point end, and obtaining a negative dip angle reflecting layer according to the left upper wave field of the seismic source end, the right lower wave field of the wave detection point end, the right upper wave field of the seismic source end and the left lower wave field of the wave detection point end; and correlating the positive inclination angle reflecting layer and the negative inclination angle reflecting layer to obtain a final diffracted wave imaging result, so that diffracted waves can be conveniently separated by utilizing characteristic differences, and accurate imaging can be realized on a diffractor.
Drawings
FIG. 1a is a schematic flow chart of an imaging method based on wavefield decomposition according to an embodiment of the present disclosure;
FIG. 1b is a flow diagram of one embodiment of the present invention;
FIG. 2 is a raw velocity field of one embodiment of the present invention;
FIG. 3 is an initial velocity field of one embodiment of the present invention;
FIG. 4 is observed seismic data (real part) of one embodiment of the invention;
FIG. 5 is observed seismic data (imaginary part) of one embodiment of the invention;
FIG. 6 is a snapshot of a wavefield of observed data 800ms for one embodiment of the present invention;
FIG. 7 is an upper left-hand wavefield snapshot of 800ms wavefield snapshot separation of one embodiment of the invention;
FIG. 8 is a lower left wavefield snapshot of 800ms wavefield snapshot separation of one embodiment of the invention;
FIG. 9 is an upper right-hand wavefield snapshot of 800ms wavefield snapshot separation of an embodiment of the invention;
FIG. 10 is a bottom right-hand wavefield snapshot of 800ms wavefield snapshot separation of one embodiment of the invention;
FIG. 11 is a schematic diagram of a positive and negative tilt angle reflective layer according to an embodiment of the invention;
FIG. 12 is a positive-angle reflective layer imaging of an embodiment of the present invention;
FIG. 13 is a negative tilt reflective layer imaging of an embodiment of the invention;
FIG. 14 is a conventional reverse time offset result for one embodiment of the present invention;
FIG. 15 is a graph showing the reverse time shift of diffracted waves according to an embodiment of the invention.
Detailed Description
For the purposes, technical solutions and advantages of the present application, the technical solutions of the present application will be clearly and completely described below with reference to specific embodiments of the present application and corresponding drawings. It will be apparent that the described embodiments are only some, but not all, of the embodiments of the present application. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are intended to be within the scope of the present application based on the embodiments herein.
In a first aspect, as shown in fig. 1a, fig. 1b is a schematic flow chart of an imaging method based on wavefield decomposition according to an embodiment of the present disclosure, including:
s101, forward continuation is carried out according to forward modeling to generate a source end wave field, and reverse continuation is carried out on the seismic record to generate a wave field of a wave point end.
Specific forward and reverse extensions can be seen in fig. 1 b. Firstly, an analytic wave field can be constructed, and forward and reverse continuation are respectively carried out according to forward numerical simulation and the acquired seismic records; the analytic wave fields of the source term and the analytic wave fields of the wave detection point end are respectively as follows:
u S for the source end wave field, f S U is a seismic wavelet excited at the source R D for wave field at detector point R Is the seismic wavelet excited by the wave detection point end.
S103, decomposing the wave field at the seismic source end to obtain a left down wave field at the seismic source end
Right lower wave field->
Left upper wave field->
And top right wavefield->
And decomposing the wave field at the wave point end to obtain a left lower wave field of the wave field at the wave point end +.>
Right lower wave field->
Left upper wave field->
And top right wavefield->
The manner of decomposition is the same for the source-side wavefield and the receiver-side wavefield, and the separation is specifically described below taking the source-side wavefield as an example.
The Hilbert transform is used here to construct the resolved wavefield (for example, the source term):
after the analytical wave field is constructed, space Fourier transformation is carried out on each time layer extrapolated by the analytical wave field, and the wave field in the time-space domain is converted into the frequency-wave number domain, so that the analytical wave field only contains positive frequency information, the direction of the wave field is judged according to the positive and negative of the space wave number, further, the up-down, left-right decomposition of the wave field is realized, and the obtained wave field is subjected to cross-correlation imaging.
The real and imaginary parts of the source-side resolved wavefield are expressed as:
in the method, in the process of the invention,
u respectively S, f S I.e. resolving the imaginary part of the wave field. The real and imaginary parts of the analytic wave field at the detector point end are respectively expressed as:
in the method, in the process of the invention,
u respectively R ,f R Hilbert transform of (C). The wave field is analyzed to only contain positive frequency w information, the wave field at each moment is respectively processed by space two-dimensional Fourier transform to be transformed into a frequency wave number domain, and the direction of the wave field is directly judged by the positive and negative of the space wave number k.
I.e. determining the arbitrary point wave field U (k) by the sign of the spatial wave number k x ,k z W) in the four directions of the two-dimensional space,
wherein U is up ,U down ,U left ,U right Is the wave field form after frequency-wave number domain conversion, w is positive frequency, k x For transverse wave number, k z For longitudinal wave number, U up Representing the upstream wave, U down Representing the downstream wave, U left Representing a left travelling wave, U right Representing the right traveling wave. />
So that each time wave field at the source end and the detector end can be decomposed into upper left, lower left, upper right and lower right wave fields and recorded separately. I.e. U (k) x ,k z The number of waves in w) satisfies U simultaneously down And U left Is determined as the left down wavefield at the source end
U (k) x ,k z The number of waves in w) satisfies U simultaneously down And U right Is determined as the right lower wavefield of the source end +.>
U (k) x ,k z Wave number in w) satisfies sum U simultaneously up U of (2) left Is determined as the upper left wavefield at the source end
U (k) x ,k z Wave number in w) satisfies sum U simultaneously up U of (2) right Is determined as the upper right wavefield of the source end +.>
The same is true for the wavefield in four directions at the detector point end.
S105, obtaining a positive dip angle reflecting layer according to the left lower wave field of the seismic source end, the right upper wave field of the wave detection point end, the right lower wave field of the seismic source end and the left upper wave field of the wave detection point end, and obtaining a negative dip angle reflecting layer according to the left upper wave field of the seismic source end, the right lower wave field of the wave detection point end, the right upper wave field of the seismic source end and the left lower wave field of the wave detection point end.
The traditional RTM zero-delay cross-correlation imaging condition formula is as follows:
to avoid low frequency noise and imaging artifacts, the wavefield is decomposed in the up and down directions, and the wavefield co-propagating at both source and detector ends is imaged in correlation:
since imaging contributions of the up-going wavefronts are not prominent in most cases, only the down-going wavefronts at both ends of the source detection are used for correlated imaging:
in the present embodiment, the specific cross-correlation means is the left down wave field at the source end and the right up wave field at the detector end and the right down wave field at the source end and the left up wave field at the detector endRespectively cross-correlating and then adding the fields to obtain a positive dip angle reflection layer, respectively cross-correlating and adding the left upper wave field at the seismic source end and the right lower wave field at the wave point end and the right upper wave field at the seismic source end and the left lower wave field at the wave point end to obtain a negative dip angle reflection layer, namely, performing cross-correlation to obtain a positive dip angle reflection layer Ill and a negative dip angle reflection layer I rr ：
The layers from the anticlockwise rotation to the right horizontal line to the obtuse angle of the reflecting layer are all positive-inclination reflecting layers, and the layers from the anticlockwise rotation to the right horizontal line to the acute angle of the reflecting layer are all negative-inclination reflecting layers.
And S107, correlating the positive inclination angle reflecting layer and the negative inclination angle reflecting layer to obtain a final diffracted wave imaging result.
I.e. adopt I diffraction ＝I rr gI ll Imaging to obtain I diffracti on is the diffraction wave reverse time shift imaging result.
Taking the positive dip angle reflecting layer as an example, under the condition that the incident wave field at the seismic source end is a downward right traveling wave, the geometric relationship shows that the emergent wave field at the wave detection end is necessarily a downward left traveling wave, namely the downward right traveling wave cannot be realized, thus I rr No image of the positive tilt reflective layer in the imaging result; when the wave field at the seismic source end is a downward left traveling wave, the wave field at the wave point end can be a downward left traveling wave, thus I ll The imaging result of (2) contains an image of the positive-angle reflective layer. Similarly, I ll No image of the negatively tilted reflective layer in the imaging result of (a), while I rr The imaging result of (2) contains an image of the negative-angle reflective layer. The diffracted wave does not conform to Snell's law, and the wave field is incident on the diffractor, which emits the diffracted wave in all directions, so that the diffractor is at I rr 、I ll And (3) performing medium-average imaging, and then imaging the diffractometer according to a diffraction wave reverse time migration imaging result formula.
By passing throughForward continuation is carried out according to forward modeling to generate a source end wave field, and backward continuation is carried out on the seismic record to generate a wave field of a wave point end; decomposing the wave field of the seismic source end to obtain a left down wave field of the seismic source end
Right lower wave field->
Left upper wave field->
And top right wavefield->
And decomposing the wave field at the wave point end to obtain a left lower wave field of the wave field at the wave point end +.>
Right lower wave field->
Left upper wave field->
And top right wavefield->
Obtaining a positive dip angle reflecting layer according to the left lower wave field of the seismic source end, the right upper wave field of the wave detection point end, the right lower wave field of the seismic source end and the left upper wave field of the wave detection point end, and obtaining a negative dip angle reflecting layer according to the left upper wave field of the seismic source end, the right lower wave field of the wave detection point end, the right upper wave field of the seismic source end and the left lower wave field of the wave detection point end; and correlating the positive inclination angle reflecting layer and the negative inclination angle reflecting layer to obtain a final diffracted wave imaging result, so that diffracted waves can be conveniently separated by utilizing characteristic differences, and accurate imaging can be realized on a diffractor.
To more specifically illustrate the method of the present invention, a three-layer depression model is used as an example (as shown in fig. 2).
Firstly, the observation system is distributed and controlled, wherein the observation system is distributed as follows: every 50 meters, 100 cannons are put on the ground surface at intervals of 50 meters at a position 500 meters away from a 0 point, each cannon is received by 600 wave detection points, and the wave detection point interval is 10 meters. The smooth velocity field (as shown in fig. 3) is then used for RTM imaging.
Then observed field data (as shown in fig. 4 and 5), the space sampling interval is 10 meters, the time sampling interval is 1 millisecond, the number of time sampling points is 2048, and the main frequency is 30 hertz. Wave equation forward extension is carried out by using a smooth velocity field, wave equation reverse extension is carried out according to a seismic record observed in the field, a wave field snapshot (shown in fig. 6) of each moment is obtained, the wave field snapshot is a wavelength snapshot recorded by a 51 st shot at 800 milliseconds, and the absorption boundary is 300 meters.
Fig. 7, 8, 9 and 10 are top left, bottom left, top right and bottom right wavefield snapshots, respectively, from which it is seen that wavefields in all directions are more clearly separated.
The left down wave field at the source end and the left down wave field at the detector end are mutually correlated to obtain an image of a positive dip reflecting layer (shown in figure 11), and the positive dip reflecting layer and a plurality of diffractors at the depressions can be seen to be imaged; and then the right down wave field at the seismic source end and the right down wave field at the wave point end are mutually correlated to obtain an image of a negative dip angle reflecting layer (shown in figure 12), and diffraction bodies at the negative dip angle reflecting layer and the depression are imaged one by one.
FIG. 14 shows the resulting diffraction wave reverse time shift imaging, and it can be seen that the four inflection points of the depression are precisely delineated and the bottom three diffractors can also be precisely imaged. Compared with the conventional RTM result of FIG. 13, the method of the invention has great reference significance, and can be used as an auxiliary means of the conventional imaging method to help better explain the condition of the underground geological structure. Therefore, compared with the prior art, the method can effectively utilize the accurate information carried by the diffraction waves to assist the conventional imaging method of oil and gas exploration, and realize high-precision amplitude-preserving imaging of the underground geological structure.
In a second aspect, corresponding, embodiments of the present application further provide a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor, wherein the processor implements the aforementioned imaging method based on wavefield decomposition when executing the program.
In this specification, each embodiment is described in a progressive manner, and identical and similar parts of each embodiment are all referred to each other, and each embodiment mainly describes differences from other embodiments. In particular, for the apparatus, device and medium embodiments, since they are substantially similar to the method embodiments, the description is relatively simple, and the relevant parts will be referred to in the description of the method embodiments, which is not repeated herein.
In this specification, each embodiment is described in a progressive manner, and identical and similar parts of each embodiment are all referred to each other, and each embodiment mainly describes differences from other embodiments. In particular, for the apparatus, device and medium embodiments, since they are substantially similar to the method embodiments, the description is relatively simple, and the relevant parts will be referred to in the description of the method embodiments, which is not repeated herein.
The foregoing describes specific embodiments of the present disclosure. Other embodiments are within the scope of the following claims. In some cases, the actions or steps or modules recited in the claims may be performed in a different order than in the embodiments and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.
Claims (4)
1. An imaging method based on wavefield decomposition, comprising:
forward continuation is carried out according to forward modeling to generate a source end wave field, and backward continuation is carried out on the seismic record to generate a wave field of a wave point end;
decomposing the wave field of the seismic source end to obtain a left down wave field of the seismic source end
Right lower wave field->
Left upper wave field
And top right wavefield->
And decomposing the wave field at the wave point end to obtain a left lower wave field of the wave field at the wave point end
Right lower wave field->
Left upper wave field->
And top right wavefield->
Obtaining a positive dip angle reflecting layer according to the left lower wave field of the seismic source end, the right upper wave field of the wave detection point end, the right lower wave field of the seismic source end and the left upper wave field of the wave detection point end, and obtaining a negative dip angle reflecting layer according to the left upper wave field of the seismic source end, the right lower wave field of the wave detection point end, the right upper wave field of the seismic source end and the left lower wave field of the wave detection point end;
and correlating the positive inclination angle reflecting layer and the negative inclination angle reflecting layer to obtain a final diffracted wave imaging result.
2. As claimed inThe method of claim 1, wherein decomposing the source-side wavefield results in a source-side lower left wavefield
Right lower wave field->
Left upper wave field->
And top right wavefield->
Comprising the following steps:
transforming the source end wave field into a frequency wave number domain wave field U (k) by performing space two-dimensional Fourier transform processing x ,k z W) determining the arbitrary point wave field U (k) by positive and negative of the spatial wave number k x ,k z W) in the four directions of the two-dimensional space,
wherein U is up ,U down ,U left ,U right Is the wave field form after frequency-wave number domain conversion, w is positive frequency, k x For transverse wave number, k z For longitudinal wave number, U up Representing the upstream wave, U down Representing the downstream wave, U left Representing a left travelling wave, U right Representing a right traveling wave;
u (k) x ,k z The number of waves in w) satisfies U simultaneously down And U left Is determined as the left down wavefield at the source end
U (k) x ,k z The number of waves in w) satisfies U simultaneously down And U right Is determined as the right lower wavefield of the source end +.>
U (k) x ,k z Wave number in w) satisfies sum U simultaneously up U of (2) left Is determined as the upper left wavefield of the source end +.>
U (k) x ,k z U of w) the number of waves simultaneously satisfying and Uup right Is determined as the upper right wavefield of the source end +.>
3. The method of claim 1, wherein obtaining a positive dip reflector from the source side down-left wavefield, the receiver side up-right wavefield, the source side down-right wavefield, and the receiver side up-left wavefield, and obtaining a negative dip reflector from the source side up-left wavefield, the receiver side down-right wavefield, the source side up-right wavefield, and the receiver side down-left wavefield, comprises:
the positive dip angle reflecting layer I is obtained by cross-correlation in the following way ll And a negative dip angle reflecting layer I rr ：
4. A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements the method of any of claims 1 to 3 when the program is executed by the processor.
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